Growth of Dunaliella tertiolecta was retarded when the alga was exposed to high boron (B) concentrations between 50 and 200 g m-³. Photosynthetic oxygen evolution as well as respiratory oxygen uptake were significantly suppressed with the rise of B concentration. Similarly the contents of chlorophyll, glycerol, lipid and proteins were lowered, while that of saccharides was raised.

DNA methylation of two repetitive sequences in tobacco nuclear genome was studied in the course ofin vitro dedifferentiation and differentiation. Using 5-mC sensitivè restriction enzymes and DNA/DNA hybridization with 25S-rDNA probe it has been shown that during the early phase of callus induction prominent changes in the methylation pattern occur which are stably maintained during subsequent callus growth. The following protoplast recovery and plant regeneration have again displayed some more modifications of the methylation status. Comparing the patterns of R₀ plants with the original plant material and the calli it can be assumed that both share in the resulting methylation status. The experiments analyzing the HRS60 family of non-transcribed highly repetitive sequences have displayed a quite monotonous methylation status thus indicating no random methylation perturbations in silent DNA sequences.

Growth ofCichorium intybus root explants was accompanied by an important increase of fresh mass during the course of callusing and rooting. The absence of glucose in callus forming medium was compensated for by hydrolysis of storage carbohydrates of the tissues, inducing a decrease in dry mass. Protein content showed similar slight variations in explants during the course of budding and callusing, whereas an important increase of protein content was found during the first 48 h in explants cultured on root forming medium.
Specific increase of soluble peroxidase activity during bud and root neoformation was found. A peak of peroxidase activity, proceeding the organ emergence, was always observed. This peak occurred earlier in bud forming than in root forming explants. Conversely, during callusing, the bulk peroxidase activity showed only weak variations, and no peak was detectable. Moreover one basic isoperoxidase was missing in these explants after a 6-d culture, whereas in both root and bud forming explants the isoperoxidase patterns were very similar. When explants growing on differentiation media were in darkness a supplementary basic isoperoxidase with the highest electrophoretic mobility was revealed.
The data obtained show that isoperoxidase patterns cannot be correlated to a particular organ differentiation process, but that peroxidase activity and especially the moment of peak emergence can be a reliable marker of the differentiation process. Moreover, light seems to inhibit the expression of a basic peroxidase in explants growing in media promoting organ differentiation.

The 18-day-old tomato vitroplants were obtained in axenic conditions by culture of expiants (including the terminal bud and the last internode of the stem) on agar-agar nutritive medium with 0 or 75 mM NaCl. The growth and the mineral content of the vitroplants were compared when the expiants were grown on media either with low or high K/Na and Ca/Na ratios, or with low K/Na and Ca/Na ratios after pretreatments of expiants by KC1, NaCl or CaCl₂ (from 0 to - 4.5 bar). The KCl pretreatment (-1.1 bar) during one day brings about an increase in vitroplant growth greater than that produced by a high Ca/Na ratio medium. The Cl accumulation was similar in expiants pretreated by KCl or NaCl. Ion content per gram of fresh matter was similar in 18-day-old vitroplants pretreated by KCl, NaCl or CaCl₂; the Na accumulation by KC1 pretreated vitroplants was not lower than that of 18-day-old vitroplants grown on a high Ca/Na ratio medium. These results show the relation between Na content of expiants and the growth of vitroplants in a NaCl medium.

Sodium chloride tolerant cell lines of finger millet were isolated from embryogenic cultures growing on MS medium supplemented with picloram (2 mg I^-1), kinetin (0.1 mg l^-1) and sodium chloride (1 %) at the end of 6 passages. The sodium chloride tolerant cell lines showed better growth in comparison with control at all concentrations of sodium chloride tested, with optimum growth at 0.25 % NaCl. When the tolerant lines were grown for 3 passages in absence of NaCl, the growth was lower than that of the tolerant lines tested immediately at the end of 6 passages of selection. NaCl tolerant calli had more Na¹ in comparison with control and they regenerated plants in presence of 1 % NaCl, while the control lines failed to differentiate. When screened in a hydroponics system with 1 % NaCl, the tolerant plants grew to maturity while the control plants failed to grow.

The effects of decreasing Ca²⁺ concentrations (Na/Ca ratios were 24, 49, 99 and 199) of the saline growth medium (NaCl concentration 200 mM) on three grass speciesCenchrus pennisetiformis Hochst. & Steud,Leptochloa fusca L. Kunth. andPcmicum turgidum Forssk. were assessed after 7 weeks growth in sand culture.L. fusca produced the highest dry biomass of all the species at varying Na/Ca ratios. Number of tillers per plant and number of green leaves per tiller were reduced significantly only inC. pennisetiformis. Leaf water potential ofC. pennisetiformis decreased at all external Na/Ca ratios, whereas inL. fusca it decreased only at an Na/Ca ratio of 99. Leaf osmotic potential ofL. fusca consistently decreased at all Na/Ca ratios, whereas that of the other two species remained unchanged. The shoot and root total sugars of all species remained unaffected at all decreasing Ca²⁺ concentrations. InP. turgidum chlorophyllb and total chlorophyll decreased consistently at all Na/Ca ratios, but inL. fusca they decreased only at the highest Na/Ca ratios. The leaf soluble proteins of all the species remained unaffected at all Na/Ca ratios. The leaf free amino acids decreased significantly inL. fusca with the increase in Na/Ca ratios. The leaf proline content was only decreased inL. fusca at the highest Na/Ca ratio. The significant correlations between the growth of the three grass species and other variables determined in this study were not found.

Effect of two different seasons and hormones on pre- and postfertilization barriers in crossability were studied inVigna mungo, V. unguiculata and their crosses. Significant differences between the two seasons for pollen fall, pollen germination, tube growth and pod set were observed. In kharif season with an average temperature of 26 to 30 °C and 75 to 85 % humidity all the characters showed higher values than in the spring season with a higher temperature of 32 to 36 °C and low humidity of 40 to 50 %. Application of gibberellic acid (GA) alone and a combination of gibberellic acid, naphthaleneacetic acid (NAA) and kinetin (KIN) significantly increased the pollen fall by 7-13 %, pollen germination by 10-12 % and pollen tube growth by 27-30 %. More pollen tube abnormalities in interspecific crosses only indicates partly incompatible reaction of pollen tube in the stylar tisue. Hormonal treatments, especially GA, significantly increased the pod set and pod harvest by 20 % and 34 %, respectively. Higher pod harvest was seen in crosses withV. unguiculata as female parent. GA treatment enhanced pollen germination and pollen tube growth, and by partially overcoming embryo abortion for 10 to 12 d, immature embryos were successfully rescued forin vitro production of hybrid plantlets.

Callus formation by fragments of cauliflower hypocotyls was favoured by raising culture medium osmolarity above -0.38 MPa. Increase in sucrose concentration while diminishing macronutrients inhibited callus initiation and growth. Root formation by the same material required a low medium osmolarity (-0.19 MPa). Reducing sucrose concentration in the classical Murashige and Skoog rooting culture medium favoured root formation. Adventitious bud formation was also depending upon medium osmolarity besides the need for a cytokinin. Reducing too much the osmotic potential of the medium had an unfavourable effect on bud neoformation. The importance of sucrose in all these processes is pointed out.

The effect of crude volatile oils extracted from the young leaves ofLantana camara var.camara was studied on the parent plant itself. The contents of water and chlorophyll, of leaves apart from seed germination, seed vigour and length of seedlings of the parent plant were adversely affected with increasing concentration of theLantana oils; this indicated autotoxic potential of the oil. The correlations between oil concentration and the studied parameters were rather strong and obeyed the concentration response relationship, typical of chemical bases. The cell respiration, however, increased with increasing concentration of the oil vapours. Compared to control, less than 13 % of the seeds of the parent plant exposed to 30 cm³ m^-3 of oil showed incipient germination with no growth of radicle beyond immeasurable protuberance, and no plumule emergence.

Chloris barbata Sw. andCyperus rotundus L. from a mercury contaminated site near a chloralkali plant were tested for relative tolerance to Hg by root-elongation method. The above two species from the Hg-contaminated site exhibited high tolerance to Hg compared to the same species from a non-contaminated site. Tolerance to Hg was higher inChloris barbata than inCyperus rotundus.

Growth and ionic relations were studied in six triticale cultivars of different geographical origins grown in a greenhouse in nutrient solution with or without the addition of 100 mM NaCl. In 21 d old plants of all the six cultivars growth was little affected in the salt treatment, whereas in the subsequent three harvests during vegetative phase (after 31, 38 and 45 d), growth reduction effects of salinity were progressively pronounced. Generally, shoots of all the six cultivars accumulated relatively more K+ as compared to Na+ or Cl-. Differential accumulation of K+, Na+ and Cl- by various cultivars was coupled with variable rates of Na+ and Cl- transport from root to shoot which were - to some extent- related to cultivar differences in growth in saline root media. Chloride content of shoots of the six cultivars was negatively correlated with the relative growth reduction due to salinity at the four harvests.

NaCl salinity affected growth, the contents of chlorophyll, carotenoids, saccharides and some minerals (Na, K, Ca, Mg, P) in wheat (Triticum vulgaris L.) plants. Irrigation of soil with CaCl₂ or KCl greatly ameliorated the adverse effects of NaCl salinity. This counteraction was associated with an increase in contents of saccharides, proteins and Ca, Mg and P which might explain their role in osmotic adjustment.

Five independent tobacco regenerant clones obtained after transformation withAgrobdcterium rhizogenes strain TR101 (four clones of the T phenotype, clone 5 a mixture of plants of the T and T' phenotypes) and untransformed plants cultivatedin vitro were gradually acclimated to the atmosphere and transferred to the soil substrate in pots. During 28 d after transplanting the increase of the leaf area was in T phenotype plants greater than in untransformed plants, but 14 d later no significant differences were observed between T phenotype and untransformed plants in leaf area and dry matter. T'phenotype plants, however, had significantly lower values in all growth parameters than T phenotype and control plants. Abaxial net photosynthetic CO₂ uptake (PN) was in both T (clones 1-4) and T' plants significantly lower than that in control and clone 5T plants. Nevertheless, due to the relatively higher adaxial PN in T plants, the total PN through both leaf surfaces was significantly lower only in clone 4 and clone 5' plants. The tendency to higher transpiration rates (E) in clones 1 - 4 in comparison with the control resulted in significant differences in water use efficiency (W.U.E.). Relatively higher E in T plants of clones 1 - 4 was connected most probably with their more developed root system (greater root dry-matter) than in untransformed plants, because no influence of the differences in stornata density on E was found.

Growth, carbon uptake and carbon utilization in leaves of various growing phase shoots (GPS) on beech trees(Fagus sylvatica L.) growing under different light conditions were compared. The values of photosynthetic capacity (maximum daily net photosynthetic rate, Pn max) were used as comparable parameters.
Daily time and irradiance (I, PhAR), when PN max was attained, were investigated similarly. Statistically significant differences were found in growth, Pn max and SLM (specific leaf mass) between different GPS and within the same stand, as well as within the same GPS and different stands. Pn max and SLM increased in the leaves of GPS I (spring - plagiotropic shoots) on trees from a sun stand from May till September. At the end of the growing season, the spring leaves exhibited, in comparison with the summer ones, intensive senescence, but leaves of the GPS II and III (summer -orthotropic shoots) evidently attained higher values of Px max and SLM at higher I (PhAR).
The correlation of growth, PN max and SLM in relation to environmental conditions, as well as the importance of transport, distribution and utilization of assimilates for annual carbon gain and biomass production are discussed in detail.

Salinity inhibited growth, and affected the contents of chlorophylls, carotenoids, saccharides, amino acids, proteins, DNA and RNA in broad bean plants. Foliar application of NaH₂PO₄ and NaNO₃ greatly ameliorated the adverse effects of NaCI. This counteraction was associated with an increase in contents of saccharides, proteins, DNA and RNA.

The relationship between photoperiodically changed growth of leaves, cotyledons, hypocotyl, roots and flowering has been investigated inChenopodium rubrum. It was found that all the growth characteristics recorded in leaves and cotyledons,i.e. length, area, dry weight and chlorophyll content, were inhibited during three inductive photoperiods (16 h darkness, 8 h light-SD) as compared with control plants grown under continuous illumination. Similarly, the cessation of root elongation and a decrease in root dry weight were observed. On the contrary, the elongation and dry weight of hypocotyl are stimulated by SD. The degree of the effect exerted by SD on the growth of different organs depends both on actual growth stage and the number of SD photoperiods. Increased relative rate of growth of roots and cotyledons was recorded in plants transferred after SD treatment to continuous illumination. However, this rise possesses only transitional character and the relative growth rate of treated plants equals that of control ones afterwards. The above growth changes are discussed as a possible modifying factor of floral differentiation.

The counteraction of exogenous L-proline at different concentrations with salinity (100 mM NaCl at sublethal concentration) were observed on germinating rice. Supplemented 30 mM L-proline was shown to be the most effective; at higher concentration it reduced seedling growth and K⁺/Na⁺ ratio. Thus 30 mM L-proline can alleviate the salinity stress in rice seedlings.

Vertical projections of nutation movements in the epicotyls of sessile oak, Turkey oak, horse chestnut and hypocotyls of European beech were recorded by means of photography and time-lapse cinematography at the early stages of their ontogeny. Attention was paid to the kinetics of growth rate, diameter of the lower part of the elongating zone, and the form, amplitude and frequency of nutation turns. At the beginning of ontogeny the vertical projection of the movements of all woody species under study was represented by irregular curves, followed by elliptical trajectories, particularly when reaching the maximum growth rate. The highest average growth rate was recorded in horse chestnut, followed by oak, and the lowest values were exhibited by beech. As to the size of amplitudes opposite results were obtained. The frequency of turns proved to be a less sensitive parameter characterizing the movement. It is suggested that the geocontrol system of horse chestnut is more effective than that of oak and, especially, of beech.

Long-term callus cultures of crownvetch (Coronilla varia L.) grown on the Murashige and Skoog's medium with 2,4-D (1 mg 1^-1) and cultures of somatic embryos cultivated on the same basic medium but with IAA (1.0 mg I^-1) were exposed to ionizing irradiation. The irradiation caused a growth inhibition excepting the lowest dose of 2.5 Gy. The highest dose of 160 Gy induced browning of the culture but this colour change was not lethal. The amount of "giant cells" present in both cultures was dependent on the dose of irradiation.

In viviparous hypocotyls ofRhizophora apiculata Blume the triacontanol treatment enhanced the growth of root and shoot (number of primary and secondary roots, length of roots, shoot height and biomass) protein and energy contents of leaves and roots,in vivo nitrate reductase activity, contents of chlorophylls and carotenoids in leaves as well as the amount of chlorophylls present in photosystems 1 and 2 and in the light harvesting complex of chloroplasts. These promotory effects were recorded at 40 and 80 mg m^-3 triacontanol, but they decreased with increasing growth regulator concentration.

Five days of suitable continuous light induced flowering in the majority ofChenopodium murale L. ecotype 197 plants as early as at the phase of the first pair of leaves. At the time of initiation of the 2nd to 4th pairs of leaves the capacity of plants to flower was reduced, the number of flowering plants being significantly lower under the same inductive light treatment. The capacity to flower increased again at the phase of the 5th and the 6th pairs of leaves. Inductive light treatment brought about a marked growth activation of organs present before induction, shoot apex elongation, precocious formation of new leaves and activation of axillary meristems. The course of these changes in plants of different age is demonstrated. The terminal flower developed during 5 short days following inductive light treatment. The paper shows similarities and differences between long-daymutale L. ecotype 197 and short-day C.rubrum L. ecotype 374 grown under practically uniform conditions.

On rooting the poplar stem cutting, the growth processes are coordinated so as to ensure optimum development of the new, vegetatively acquired individual. At first, adventitious roots develop on the cutting from latent root primordia. A part of them is short-lived, but in the meantime other, the so-called wound adventitious roots initiate from the callus on the lower cut surface of the cutting, which complement the permanent root system. In this way, conditions are prepared for a rapid growth and development of the stem, which forms from the upper bud on the cutting. The action of apical meristems providing the elongation of the stem and root, is followed by the action of vascular cambium. By the radial growth of organs controlled by cambium, the capacity of substance transport increases relatively to progressing development of the new plant. In the buried stem cutting cambium is the first to start functioning. Its reactivation is slow, discontinuous, and at the beginning it depends on local stimulating sources of the cutting itself. It was observed for the first time that, in addition to expanding buds, activated root primordia are also such sources of stimuli. The overall induction of cambial activity in the cutting occurs only in the period of rapid growth and development of the new stem, which thus becomes the main source of factors controlling the cambial activity of the cutting. In comparison with the growth of stem and cutting, the radial growth of adventitious roots is limited and there are considerable differences in the thickness of radial increments between individual roots.

Diurnal variations in endogenous IAA levels inFatsia japonica leaves, maintaining constant other external factors such as temperature and relative humidity, were studied. Plants were cultivated in a growth chamber (20 °C, 75 % RH, 16 h photoperiod, 400 µmol m^-2 s^-1 PAR). IAA analyses were carried out by analytical IP-HPLC with on-line spectrofluorimetry. Rhythmic variation of endogenous IAA levels was found. At the onset of the light period the IAA concentration dropped very rapidly from 1070 pmol g^-1 (fr.m.) to 144 pmol g^-1 (fr.m.). This concentration was nearly constant throughout the entire light period. During the subsequent dark period the IAA levels increased again to about 1000 pmol g^-1 (fr.m.) at the end of the dark phase. These results were not confirmed in open field conditions where many other external factors probably influence the endogenous IAA content.

The effect of indol-3-ylacetic acid, gibberellie acid, kinetin, abscisic acid and Ethrel on the growth of mycelium, sporulation and germination of spores ofFusarium culmorum of different pathogenicity to wheat seedlings was studied. The production of gibberellins, auxins, cytokinins, ethylene and growth inhibitors by these isolates was determined as well. It has been found that most pronounced and explicit effect on growth and development in fungi was produced by Ethrel which strongly inhibited these processes. ABA proved to be a strong growth and development stimulator, though to a different extent in different isolates. GA₃ strongly stimulated sporulation and spore germination in some isolates. The effect of IAA and K on growth and development in fungi was slight. More sensitive to growth regulators were the fungi in earlier stages of growth. No correlation between the pathogenicity of the isolates and their ability to produce growth regulators as well as between their susceptibility to exogenous growth substances in the processes of fungal growth and development was stated.

Salinity had generally little influence on the water content of different parts of cowpea(Vigna sinensis L.), calabrese(Brassica oleracea L. var.botrylis) and red radish(Raphanus salivus L.) plants. Salinity showed a promotive effect on the growth of cowpea, while in calabrese the effect was either promotive or depressive depending upon the concentration of the NaCl, and in red radish plants salinity progressively suppressed growth.
Total nitrogen, phosphorus, potassium and sodium contents of cowpea leaves were not affected by salinity treatments, while in calabrese and red radish leaves the contents of N, P and K were generally decreased as the salinity level increased. Gibberellin (GA₃) applied to salt-treated plants had either a stimulatory or inhibitory effect on the growth, water content and contents of N, P, K and Na in the leaves depending upon the plant type, the concentration of GA₃ and level of salinity.

Growth of nine field grown cowpea genotypes was characterized using plastochron index. Attainment of the final plastochron index was considered as a point of completion of a vegetative phase. The population under study completed a vegetative phase within 50 d and exhibited flower initiation in 55 d. The gap between completion of the vegetative phase and flower initiation indicated the prevalence of juvenility in cowpea. The maturity period was found to be a sum of the periods for plastochron completion, lag I, pod development and lag II. Lag I and Lag-II periods existed due to variation in the relative sensitivity of successively formed leaves to the normal inductive conditions. A high genotypic variation for the two lag periods indicated a scope for designing an efficient plant architecture of cowpea either for grain or for vegetable purpose.

The effects of Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ on growth and the biochemical characteristics of photosynthesis were more expressed in barley (Hordeum vulgare L.) than in maize (Zea mays L.) seedlings. The barley and maize seedlings exhibited retardation in shoot and root growth after exposure of Cu²⁺, Cd²⁺ and Pb²⁺. The Zn²⁺ions practically did not influence these characteristics. The total protein content of barley and maize roots declined with an increase in heavy metal ion concentrations. The protein content of barley shoots was only slighly decreased with an increase in heavy metal ion concentrations, but the protein content in maize shoots was increased under the same conditions. The chlorophyll content was decreased in barley shoots and increased in maize. The ribulose-l,5-bisphosphate carboxylase (RuBPC, EC 4.1.1.39) and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) activities were decreased drastically by Cu²⁺, Cd²⁺ and Pb²⁺ in thein vivo experiments. The tested heavy metal ions affect photosynthesis probably mainly by inhibition of these key carboxylating enzymes: this mechanism was studied in thein vitro experiments.

The main scientific results achieved in individual departments of the Institute of Experimental Botany during 30 years of its existence are briefly summarized. They include methods of studying photosynthesis, ontogenetic changes of photosynthetic characteristics, stress factors affecting photosynthetic activities, photosynthesis of transgenic plants and duringin vitro cultivation, roles of auxins and cytokinins in plant growth and development, development and testing of new plant growth regulators, models of organogenesisin vitro, metabolic and mutagenic activities of phenolic substances, hormonal regulation of flowering, activities of promutagens (nitrosamines, 7,12-dimethylbenzanthracene), model systems of genetic damage, repair synthesis and post-replication repair, developmental pollen biology and biotechnology, extracellular nucleolytic activity of pollen, selection of apple scab immune cultivars of apple tree, chemotaxonomy ofFabaceae andAllium species, selection pressures in embryoids, somatic embryogenesis and nuclear genome changes in plant cell and callus cultures, discoveries of new plant viruses, virus spread and persistence in crops, development of polyclonal and monoclonal antibodies, role of oxidative pentosephosphate cycle in biosynthesis of viral RNA, and virus diseases of forest trees.

The partitioning of¹⁴C-assimilates was studied in pigeonpea(Cajanus cajan L.) at vegetative and flowering stages (40 and 70 d after sowing, respectively) exposed to moderate and severe drought induced by withholding the irrigation. At vegetative stage, the ethanol soluble fraction in shoot decreased from 99 to 43.16 % between 0 and 120 h, whereas in underground part it increased from 1% to 56.84 % with maximum amount in nodules (35.51 %). Similar trend was observed in ethanol insoluble fraction. At moderate drought, a significant increase in soluble fraction (11.31 %) in nodules was observed. Stem showed significant reduction of assimilates (13.09 %). After flowering, the assimilates produced in leaves were exported to reproductive parts, especially under drought. In plants recovering from severe drought, 14C in soluble and insoluble fractions in reproductive parts was reduced to 85 % and 43 %, respectively, whereas leaf and nodules showed a significant increase. Thus the assimilate partitioning to different plant parts was dependent on growth stage and affected by drought.

Glutamate dehydrogenase (GDH) activity, protein and total nitrogen contents in the secondary leaves of maize(Zea mays L. cv. Ganga Safed-2) seedlings increased during early seedling growth and then declined after reaching a peak level at either 10 d (GDH) or 12 d (metabolites). While the effect of kinetin on enzyme activity was statistically insignificant, benzyladenine supplied with nutrient solution increased GDH activity in secondary leaves of both 10-d as well as 14-d seedlings. However, both growth regulators increased the contents of total soluble proteins, total nitrogen, chlorophyll(a+b) and carotenoids in both 10 and 14-d old leaves.